This invention relates to an automatically controlled robot (mechanical mechanism) having substantially improved capacity for transferring semiconductor wafers between stations in processing equipment for the manufacture of semiconductors.
In the manufacture of semiconductors, such as integrated circuits (ICs), dynamic random access memories (DRAMs), etc., large thin wafers (typically of silicon) from which the semiconductors are fabricated must frequently be transferred from one processing chamber to another. This transfer of wafers must be carried out under conditions of absolute cleanliness and often at sub-atmospheric pressures. To this end various mechanical arrangements have been devised for transferring wafers to and from processing chambers in a piece of equipment or from one piece of equipment to another.
It is the usual practice to load wafers into a cassette so that a number of them can be carried under clean-room conditions safely and efficiently from one place to another. A cassette loaded with wafers is then inserted into an input/output (I/O) chamber (xe2x80x9cload lockxe2x80x9d chamber) where a desired gas pressure and atmosphere can be established. The wafers are fed one-by-one to or from their respective cassettes into or out of the I/O chamber. It is desirable from the standpoint of efficiency in handling of the wafers that the I/O chamber be located in close proximity to a number of processing chambers to permit more than one wafer to be processed nearby and at the same time. To this end two or more chambers are arranged at locations on the periphery of a transfer chamber which is hermetically sealable and which communicates with both the I/O chamber and the processing chambers. Located within the transfer chamber is an automatically controlled wafer handling mechanism, or robot, which takes wafers supplied from the I/O chamber and then transfers each wafer into a selected processing chamber. After processing in one chamber a wafer is withdrawn from it by the robot and inserted into another processing chamber, or returned to the I/O chamber and ultimately a respective cassette.
Semiconductor wafers are by their nature fragile and easily chipped or scratched. Therefore they are handled with great care to prevent damage. The robot mechanism which handles a wafer holds it securely, yet without scratching a surface or chipping an edge of the brittle wafers. The robot moves the wafer smoothly without vibration or sudden stops or jerks. Vibration of the robot can cause abrasion between a robot blade holding a wafer and a surface of the wafer. The xe2x80x9cdustxe2x80x9d or abraded particles of the wafer caused by such vibration can in turn cause surface contamination of other wafers, an undesirable condition. As a result the design of a robot requires careful measures to insure that the movable parts of the robot operate smoothly without lost motion or play, with the requisite gentleness in holding a wafer, yet be able to move the wafer quickly and accurately between locations. Because of these complex requirements, previous robot mechanisms have been unable to handle more than one wafer at a time in the limited space provided within a reasonably sized transfer chamber. It is desirable to provide a robot able to independently handle two wafers at the same time thereby increasing the through-put of a wafer-processing apparatus. It is also desirable to be able to place such a dual-capacity robot within substantially the same size of transfer chamber as used with previous robots. This also permits ease of fitting a dual-capacity robot into wafer processing apparatus of prior design and size.
In accordance with the present invention, in one specific embodiment thereof, there is provided an improved robot for handling semiconductor wafers and having twice the wafer-moving and transfer capability of previous robots. This improved robot includes a first arm assembly having a left and a right arm each mounted at one end for independent rotation in a first horizontal plane about a center vertical axis, the other ends of the arms being movably joined together and holding a blade on which a wafer can be carried, the arms being horizontally bendable near their centers so they can be folded to retract the blade toward the center axis and rotated to a desired angular position, the arms being extendable from the center axis by moving the arms together near their centers to bring the arms toward each other and to extend the blade from the center axis by a desired amount. The robot further includes a second arm assembly substantially identical to the first assembly and rotatable in a second horizontal plane closely spaced above the first plane, the operation of the second assembly being substantially identical to that of the first assembly but independent thereof.
A better understanding of the invention together with a fuller appreciation of its many advantages will best be gained from a study of the following description given in conjunction with the accompanying drawings and claims.